Carbon nanotubes in various forms have been widely written about and disclosed. They have been reported to and provide significant improvements in mechanical strength and electrical properties to materials when properly dispersed in a discrete manner and well adhered or bonded to the matrix. Carbon nanotubes have surface areas in the range of about 100 m2/gram for multiwall carbon nanotubes to about 2000 m2/gram for single wall carbon nanotubes. These large surface areas are conducive to attach or associate medicaments. Even more useful would be to use the interior of the carbon nanotubes as vesicles for molecules. However, these carbon nanotubes, as made, are in the form of clusters like a bird's nest, or fibrils that consist of many tubes that are “clumped” together, making them less than ideal or even useful to be able to reach their full performance potential. The carbon nanotubes as made have closed ends thereby restricting access to the interior cavities. Carbon nanotube aggregations are unable to form uniform, homogeneous dilute solutions for injection or treatment of the human body. Discrete carbon nanotubes solve these problems because the tubes are separate and distinct from each other and can be maintained in that form without re-agglomerating in aqueous media. For drug delivery applications, is also desirable for the carbon nanotubes to flow through the fine needle or injection device with relative ease.
For drug delivery in the human body carbon nanotube surfaces have to be modified to increase their hydrophilicity to be able to be dispersed in the aqueous medium.
Furthermore, the surface modification or functionalization is required to enable biocompatibility and low toxicity for their medical applications.
The functionalization procedure of CNTs can be divided into two main approaches, that is, chemical bond attachment (covalent or ionic) and noncovalent or associative attachment (physioadsorption or physioabsorption).
If the drug is to be contained within the discrete carbon nanotube it may also considered to be important to treat the inside surface of the tube and/or the ends of the discrete tube to control the rate of inclusion of the drug molecule as well as the release rate of the drug molecule from the interior cavity. Selection of discrete carbon nanotubes, carbon nanotube length, diameter, and degree and type of functionalization are important parameters to control the kinetics of drug delivery. In some cases it may also be desirable to have the functionalization to include targeting molecules to specific target locations such as tumors.
A particular challenge with nanotubes is to effectively incorporate a drug inside the tube with little or no amount of the same drug on the outside of the tube.